OK, so I got the latest (yesterday's) FAQ. Hopefully it's not too late. :)
I like the new split for this information, but there are a lot of facts
reversed (with levels and groups). Here's an update.
Frank

--- newnewFAQ.xhtml 2004-11-10 19:37:31.000000000 +0100
+++ mynewnewFAQ.xhtml 2004-11-10 21:15:18.000000000 +0100
@@ -1017,54 +1017,57 @@
class="command">setxkbmap</code> command, which in turn depends on <code
class="command">xkbcomp</code>, the XKB data files, and the X libraries.</p>
-<p>Many users of the X Window System, particularly outside the United States,
-find that they need support for multiple <em>group</em>s on their keyboards.
-A group a set of two keyboard symbols paired so that pressing an unshifted key
-gets you the first symbol in the group, and pressing the same key with the
-<code>Shift</code> key held down give you the second symbol in the group.</p>
-
-<p>A U.S. keyboard has only one group &mdash; this is sufficient to type all of
-the symbols in the ASCII character set. Elsewhere in the world, however,
-keyboards frequently have keys engraved with more than two glyphs. A third and
-often a fourth glyph appear. These comprise the <em>alternate group</em>, which
-is usually accessed with a modifier key not found on most U.S. keyboards:
-<code>AltGr</code>. When the <code>AltGr</code> key is pressed, the third and
-fourth glyphs on the keycap can be entered: <kbd>AltGr + <em>key</em></kbd>
-gives you the third, and if a fourth is engraved, it is entered with <kbd>AltGr
-+ Shift + <em>key</em></kbd>. For example, on many European keyboards, one can
-press <kbd>AltGr + E</kbd> to produce the Euro sign (&euro;). Sometimes the
-<code>Alt</code> key on the right-hand side of the keyboard is used as
-<code>AltGr</code> if there is no key actually engraved with
-<code>AltGr</code>.</p>
-
-<p>If even an alternate group does not suffice to let users type all of the
-symbols they need to, the entire keyboard mapping can be switched out with a
-single keystroke using what the X KEYBOARD Extension (XKB) refers to as a
-"level". This is typically done with a <code>Mode Switch</code> key, which is
-somewhat analogous to <code>Caps Lock</code>. When this key is pressed, the X
-Window System toggles the second level. This approach is often taken with
-keyboards that need to type in both the Cyrillic and Latin alphabets. A Russian
-user, for example, might use a French keyboard layout (complete with alternate
-group symbols) on the first level to correspond with Western European friends
-via email, but then press <code>Mode Switch</code> to change to the second
-level, featuring Cyrillic letters, to write messages to Russian friends.</p>
-
-<p>XKB supports up to four keysyms per level (two groups of two symbols each),
-and up to four levels. In such situations, rather than having a <code>Mode
-Switch</code> key, there might be <code>Next Mode</code> and <code>Previous
-Mode</code> keys that cycle through the available levels.</p>
-
-<p>A U.S. keyboard, even if keys are remapped so that <code>AltGr</code> and/or
-<code>Mode Switch</code> keys are available, does not acquire much meaningful
-additional functionality unless an alternate group and/or multiple levels are
-defined in software, so that "the keys know what to do" when the alternate group
-is activated or the level is changed.</p>
+<p>Many non-US keyboards need to support more than two glyphs per key.
+On a typical U.S. keyboard, there are at most two glyphs on each keycap
+&mdash; one is accessed with a <code>Shift</code> or <code>Caps Lock</code>
+key, and one without. To enable access to third, fourth, or fifth glyphs,
+other modifiers are used.</p>
+
+<p>PC Keyboards for Latin-script characters ususally have an <kbd>AltGr</kbd>
+(alternate graphic) key that replaces the right <kbd>Alt</kbd> key. When a
+key is pressed while the <kbd>AltGr</kbd> key is down will generate the
+third glyph, and when <kbd>Shift</kbd> <em>and</em> <kbd>AltGr</kbd> are down,
+it will generate the fourth glyph. For example, on many European keyboards,
+one can press <kbd>AltGr + E</kbd> to produce the Euro sign (&euro;).
+Sometimes the <kbd>Alt</kbd> key on the right-hand side of the keyboard
+is used as <kbd>AltGr</kbd> if there is no key actually engraved with
+<kbd>AltGr</kbd>.</p>
+
+<p>Non-Latin keyboards can have most of the keys engraved with non-Latin
+<em>and</em> Latin glyphs. For example, Russian keyboards often work this
+way because they must support both the Latin and Cyrillic alphabets.
+As a consequence, users of the X Window System need a way to <em>combine
+layouts</em>. Combined layouts are often useful for users who need to type
+in both the Cyrillic and Latin alphabets. A Russian user might use a French
+keyboard layout (complete with third and fourth glyphs) to correspond with
+Western European friends via email, but then switch to another layout with
+Cyrillic letters to write messages to Russian friends.</p>
+
+<p>There are two ways to specify a more than two glyphs: levels or groups.
+The core X protocol uses groups, but XKB now uses levels. XKB changed in order
+to better support combined layouts. To specify a third glyph with groups,
+a second group is assigned to a key and the glyph is assigned to the first
+shift-level of the second group. To use levels, a third level is assigned to
+a key. The keysym used to generate these third glyphs also changes. With groups
+the <kbd>AltGr</kbd> key is assigned <code>Mode_switch</code>, and with
+levels it gets <code>ISO_Level3_Shift</code>. By moving from the muliple-group
+to the shift-level method, combined layouts become much more flexible and
+easier to maintain. With the old multiple-group approach, it was impossible
+to combine layouts that had more than two glyphs per key.</p>
+
+<p>XKB supports up to four keysyms per group and up to four groups per layout.
+In situations with three or four groups, rather than using
+<code>Mode_switch</code>, there might be <code>ISO_Next_Group</code> and
+<code>ISO_Prev_Group</code> used that cycle through the available
+groups.</p>
<p>A separate approach to typing symbols not engraved on the keyboard is to use
-the <code>Multi_key</code>. This enables you to use two keys to type any symbol
-defined by Compose sequences for your locale. For most layouts, the
-<code>Multi_key</code> keysym is bound to <kbd>Shift + AltGr</kbd>. Note that
-<kbd>AltGr + Shift</kbd> means something else; see above.</p>
+<em>compose sequences</em>. Using <code>Multi_key</code> enables two keys to
+generate any symbol defined by Compose sequences for your locale. So to type
+&Ccedil; in the C locale, first type <code>Multi_key</code>, then
+<code>comma</code> followed by capital <code>C</code>. The order of the
+<code>comma</code> and <code>C</code> can be reversed. Yet another way to
+define these kinds of symbols is with the XIM extension.</p>
<h3><a id="xfree86_3x">What is the story with XFree86 3.<em>x</em>?</a></h3>